Osteogenesis Imperfecta

Description

Osteogenesis imperfecta (OI) literally means imperfectly formed bones. People with OI have an error (mutation) in the genetic instructions on how to make strong bones. As a result, their bones break easily.

Risk Factors/Prevention

If one parent has OI, each of their children has a 50 percent chance of being born with OI. But the child's symptoms and degree of disability could be very different than the parent's. In some cases, neither parent has OI, and the genetic defect is a spontaneous mutation.

Symptoms

What happens

One of the genes that tells the body how to make a specific protein (type I collagen) is defective in people with OI. Type I collagen is a major component of the connective tissues in bones, ligaments, teeth, and the white outer tissue of the eyeballs (sclera). As a result of the defect, the body may not produce enough type I collagen or it may produce poor quality collagen. The result in both cases is the same: fragile bones that break easily. However, the bones heal at a normal rate.

OI is a relatively rare disorder. Ultrasound can often detect severe cases of OI during pregnancy. Genetic testing may be able to identify the mutation, particularly if the parent's mutation is also known. But in many cases, bone fractures that occur with little or no trauma are often the first indication that a person has OI.

Forms of OI

There are four recognized types of OI, which vary in severity and characteristics. Several other conditions are also associated with OI, including short stature, a triangular face, respiratory problems and hearing loss. Each person with OI may have a different combination of clinical characteristics.

Type I is the most common and mildest type of OI. The collagen structure is normal, but there is less collagen than normal. There is little or no bone deformity, although bones are fragile and easily broken. The effects of OI may extend to the teeth, making them prone to cavities and cracking. The whites of the eyes may have a blue, purple or gray tint.

Type II is the most severe form of OI. The collagen is improperly formed. Bones may break even while the fetus is in the womb, and many infants are stillborn or die shortly after birth.

Type III OI also has improperly formed collagen and often severe bone deformities. The infant is often born with fractures. The whites of the eyes may be white, blue, purple or gray. People with type III OI are generally shorter than average and may have spinal deformities, respiratory complications and brittle teeth.

Type IV OI is moderately severe, with improperly formed collagen. Bones fracture easily, but the whites of the eyes are normal. Some people with type IV OI may be shorter than average and may have brittle teeth. Bone deformities are mild to moderate.

Treatment Options

There is no cure for OI. Treatment must be individualized and depends on the severity of the disease and the age of the patient. Care is provided by a team of health-care professionals, including several types of doctors, a physical therapist, a nurse-clinician and a social worker. Treatment goals include:

Maximizing function
Minimizing disability
Fostering independence and social skills
Maintaining overall health

Most treatment, even of fractures, will be nonsurgical. Casting, bracing or splinting the fracture is necessary to immobilize the bone so that healing can occur. But long periods of immobilization can decrease mobility and increase the risk of future fractures. For that reason, orthopaedists will encourage movement and weight bearing as soon as possible after the fracture.

Precautions

Here are some tips developed by the Osteogenesis Imperfecta Foundation for dealing with children with OI.

Don't be afraid to touch or hold an infant with OI, but be careful. Never lift a child with OI by holding him or her under the armpits. Do not pull on arms or legs or lift the legs by the ankles to change a diaper. To lift an infant with OI, spread your fingers apart and put one hand between the legs and under the buttocks; place the other hand behind the shoulders, neck and head.
Do not feel guilty if a fracture does occur. Children must develop and fractures will occur no matter how careful you are.
Select an infant car seat that reclines. It should be easy to place or remove the child in the seat. Consider padding the seat with foam and using a layer of foam between the child and the harness.
Be sure your stroller is large enough to accommodate casts. Don't use a sling or umbrella-type stroller.
Follow your doctor's instructions carefully, especially with regard to cast care and mobility exercises. Swimming and walking are often recommended as safe exercises.
Avoid activities such as smoking, drinking and taking steroids because they have a negative impact on bone density.
Increasing awareness of child abuse and a lack of awareness about OI may lead to inaccurate conclusions about a family situation. Always have a letter from your family doctor and a copy of your child's medical records handy.

Treatment Options: Surgical

Repeated fractures of the same bone, deformity, or fractures that do not heal properly are all indications that surgery may be necessary. Metal rods may be inserted in the long bones of the arms and legs. Some rods are a fixed length and must be replaced as the child grows. Other rods are designed like telescopes so they can expand along with the bone growth. However, other complications may occur with telescoping rods. Do not hesitate to ask your orthopaedic surgeon about both options.

In many children with OI, the incidence of fractures decreases significantly as the child matures. However, the brittle bone syndrome may become active again after a woman reaches menopause or a man attains age 60.

Scoliosis, or curvature of the spine, is a significant problem for many children with OI. Bracing is the normal treatment for scoliosis, but it is often ineffective in children with OI. Spinal fusion, in which one or more of the vertebra are straightened and fused together, is often recommended to prevent excessive curvature.

Research on the Horizon/What's New

Research into other treatment methods is continuing. Several clinical trials are focused on the use of medications to improve bone strength and decrease fracture rates. Pamidronate (a bisphosphonate) has been found to inhibit bone resorption. As a result, chronic bone pain lessens, bone density increases, fewer fractures occur and mobility improves. More promising research is being done in the area of gene therapy. It may be possible to replace the damaged cells with normal cells or to suppress the mutation completely. However, it may be some time until these approaches are approved for use.

November 2004